If it's a gray or white, fuzzy patch then it is most likely fungus. It's very common in softshells and is one of the lead causes of death in hatchlings, especially the Florida softshell which seems especially prone. First, I suggest raising the temperature in your softies aquarium in the 80-85 F range. Second, purchase a treatment found in fish stores that is used to treat a disease called "Ick" (a common fungus ailment for freshwater fish). You will be surprised...ask any fish store and they will most likely carry Ick medicine which is a malachite green formula. This blue liquid should be added to your aquarium as directions on the bottle will provide. This should take care of the problem. Afterwards, I suggest purchasing "Dr. Turtle." Many pet stores carry it...it is a white, turtle shaped block that dissolves slowly in your aquarium that kills bacteria and fungus. A great preventive measure. Although not so great if you have an undergravel filter...it could kill the helpful bacteria that aid in filtiration. Also, be sure to keep the tank thoroughly cleaned and remove anything sharp that could scratch your softies shell. Scratches often lead to fungus. Good luck, and if you are unable to find any Ick medicine to use on your tank, let me know and I can tell you how to treat the fungus with a salt solution bath for your turtle. Although it is more time consuming, and I find the ick medicine has better results.